Hydration, micellar

Figure 12.7 Relative viscosity r)r = versus hydrated micellar volume fraction

We also proposed a novel light scattering intensity analysis mefood, which is, valid up to about 50% hydrated micellar volume fraction. The new light scattering intensity analysis method significantly extends the concentration range of the traditional Zimm Plot (24). Its simplicity makes it useful also as a fingerprint to detect phase transitions. 

Perhaps the simplest modification of Nafion for DMFCs was carried out by Tricofi [28], who doped Nafion 117 with Cs cations. The decrease in size of hydrated micellar domains, upon snbstituting a portion of the membranes sulfonate sites with cesium, caused the methanol permeability to fall. The ratio of proton conductivity to methanol permeability, which reflects membrane selectivity, increased by a factor of 2.5 when Nafion 117 in the H+ form was fnlly exchanged with cesium. To prevent cesium fiom leaching ont of the membrane during fuel cell operation, Tricofi proposed adding a suitable amount of Cs salt to the methanol/water feed mixture. 

The majority of practical micellar systems of Tionnal micelles use water as tire main solvent. Reverse micelles use water immiscible organic solvents, altlrough tire cores of reverse micelles are usually hydrated and may contain considerable quantities of water. Polar solvents such as glycerol, etlrylene glycol, fonnamide and hydrazine are now being used instead of water to support regular micelles [10]. Critical fluids such as critical carbon dioxide are... 

In this study we examined the influence of concentration conditions, acidity of solutions, and electrolytes inclusions on the liophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 at the cloud point temperature. The liophilic properties of micellar phases formed under different conditions were determined by the estimation of effective hydration values and solvatation free energy of methylene and carboxyl groups at cloud-point extraction of aliphatic acids. It was demonstrated that micellar phases formed from the low concentrated aqueous solutions of the surfactant have more hydrophobic properties than the phases resulting from highly concentrated solutions. The influence of media acidity on the liophilic properties of the surfactant phases was also exposed. 

As mentioned above, water structure in reversed micelles deviates considerably from the structure in the bulk-phase. Therefore, the hydration shell of macromolecules entrapped in reversed micellar systems should be changed and thus also their conformation. According to the results of several authors this is indeed the case. 

The former investigation was motivated, in part by the fact that in a previous study (7) there had been a marked difference on the rates of reactions of e (aq) and U(VI) between homogeneous solutions and those containing micellar material. When the rate of disappearance of the hydrated electron is measured over a range of concentrations from 2 x 10-5 M to 8 x 10-lt M at pH = 9.7 in solutions formally 0.003 M Si02, the calculated second order rate parameter is 1.4 x 109 M-1s-1. This is a marked decrease from any of the previous measurements and emphasizes the point that the prediction of Pu chemistry in a natural water system must take cognizence of factors that are not usually deemed significant. 

A rather nnexpected solnbilization phenomenon has also been described, i.e., the pressnre-indnced encapsnlation of low-molecnlar-weight gases in the aqneons micellar core, followed by clathrate hydrate formation [144,145],... 

Some investigations have emphasized the importance of micellar size as a control parameter of nanoparticle size [224]. It has been suggested that other factors also influence the nanoparticle size, such as the concentration of the reagents, hydration of the surfactant head group, intermicellar interactions, and the intermicellar exchange rate [198,225-228],... 

By swelling with aqueous electrolyte, cations (and, to lesser extent, also anions) penetrate together with water into the hydrophilic regions and form spherical electrolyte clusters with micellar morphology. The inner surface of clusters and channels is composed of a double layer of the immobilized —SO3 groups and the equivalent number of counterions, M+. Anions in the interior of the clusters are shielded from the —SOJ groups by hydrated cations and water molecules. On the other hand, anions are thus... 

The rate of attack of water upon the tri-/>-anisylmethyl cation is unaffected by binding of this cation to anionic micelles of sodium dodecyl sulfate (SDS) (Bunton and Huang, 1972) and equilibrium constants for aldehyde hydration are only slightly reduced by binding to micelles (Albrizzio and Cordes, 1979). These observations are also consistent with substrate binding at a wet micellar surface rather than in the interior of the micelle. 

The Krafft Point may be defined as the temperature above which the solubility of a surfactant increases steeply. At this temperature, the solubility of the surfactant becomes equal to the critical micelle concentration (Cj ) of the surfactant. Therefore, surfactant micelles only exist at temperatures above the Krafft Point. This point is a triple point at which the surfactant coexists in the monomeric, the micellar, and the hydrated solid state (, ). 

For pure nonionic EO adducts, increase in the number of oxyethylene groups in the molecule results in a decrease in the tendency to form micelles and an increase in the surface tension of the solution at the critical micelle concentration (1 ) (l. ) This change in surface activity is due to the greater surface area of the molecules in the adsorption layer and at the micellar surface as a result of the presence there of the highly hydrated polyoxyethylene chain. The reduction in the tendency to form micelles is due to the increase in the free energy of micelle formation as a result of partial dehydration of the polyoxyethylene chain during incorporation into the micelle ( 1 6) (17). 

The temperature, abbreviated c.m.t., at which a deter-gent/solvent system or a lipid/solvent system passes from a hydrated crystalline state to an isotropic micellar solution. For a number of lipids, the c.m.t. is below the freezing point of the solvent. The Krafft point,, is the c.m.t. at the critical micelle concentration. 

It is noteworthy that the indenyl complex RuCl(ri -C9H7)(PPh3)2l4 provides an efficient catalyst precursor for the anti-Markovnikov hydration of terminal alkynes in aqueous media, especially in micellar solutions with either anionic (sodium dode-cylsulfate (SDS)) or cationic (hexadecyltrimethylammonium bromide (CTAB)) surfactants [38]. This system can be applied to the hydration of propargylic alcohols to selectively produce P-hydroxyaldehydes, whereas RuCl(Cp)(PMe3)2 gives a,P-unsat-urated aldehydes (the Meyer Schuster rearrangement products)(Scheme 10.8) [39]. 

Another synthetic polymer that has shown promise in recent clinical trials for the micellar encapsulation of anticancer dmgs is a block copolymer of PEG and poly (aspartic acid) [PEG-Z -P(Asp)]. Doxombicin can be covalently attached to PEG-fi-P(Asp) through the free carboxylic acid groups on aspartic acid, and the block copolymer then forms micelles in solution with the hydrophobic aspartic acid and dmg block forming the core (Yokoyama et al. 1991 Kataoka et al. 1993). As typically occurs, the hydrated PEG chains significantly increased blood circulation... 

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